Green Sea Turtle
The Green sea turtle (Chelonia mydas) or green turtle is a large sea turtle of the family Cheloniidae. It is the only species in the genus Chelonia.[1] Its range extends throughout tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans.[2] Their common name derives from the usually green fat found beneath their carapace (upper shell). The green sea turtle is a sea turtle, possessing a dorsoventrally flattened body covered by a large, teardrop-shaped carapace and a pair of large, paddle-like flippers. It is usually lightly colored, although parts of the carapace can be almost black in the eastern Pacific. Unlike other members of its family, such as the hawksbill sea turtleand loggerhead sea turtle, C. mydas is mostly herbivorous. The adults commonly inhabit shallow lagoons, feeding mostly on various species of seagrasses.[3] Like other sea turtles, they migrate long distances between feeding grounds and hatching beaches. Many islands worldwide are known as Turtle Island due to green sea turtles nesting on their beaches. Females crawl out on beaches, dig nests and lay eggs during the night. Later, hatchlings emerge and walk into the water. Those that reach maturity may live to age 80 in the wild.[2] C. mydas is listed as endangered by the IUCN and CITES and is protected from exploitation in most countries. It is illegal to collect, harm or kill them. In addition, many countries have laws and ordinances to protect nesting areas. However, turtles are still in danger because of several human practices. In some countries, turtles and their eggs are hunted for food. Pollution indirectly harms turtles at both population and individual scales. Many turtles die caught in fishing nets. Also, real estatedevelopment often causes habitat loss by eliminating nesting beaches. Taxonomy The green sea turtle is a member of the tribe Chelonini. A 1993 study clarified the status of genus Chelonia with respect to the other marine turtles. The carnivorousEretmochelys (hawksbill), Caretta (loggerhead) and Lepidochelys (Ridley) were assigned to the tribe Carettini. Herbivorous Chelonia warranted their status, while Natator (flatback) was further removed than previously believed.[4] The species was originally described by Linnaeus in 1758 as Testudo mydas.[5] In 1868,Bocourt named a particular species of sea turtle as Chelonia agassizii (Chelonia agassizi''is a commonly cited misspelling of this taxon).[6] This "species" was referred to as the "black sea turtle".[7] Later research determined the "black sea turtle" was not genetically distinct from ''C. mydas, and thus taxonomically not a separate species.[8] These two "species" were then united as Chelonia mydas and were given subspecies status. C. mydas mydas referred to the originally described population, while C. mydas agassizi''referred only to the Pacific population.[9][10] This subdivision was later determined to be invalid and all species members were then designated ''Chelonia mydas.[1] The oft-mentioned name C. agassizi remains an invalid junior synonym of C. mydas. The species' common name does not derive from any particular green external coloration of the turtle. Its name comes from the greenish color of the turtles' fat, which is only found in a layer between their inner organs and their shell.[11] As a species found worldwide, the green turtle is called differently in some languages and dialects. In the Hawaiian language, honu is used to refer to this species.[12] Description Its appearance is that of a typical sea turtle. C. mydas has a dorsoventrally flattened body, a beaked head at the end of a short neck, and paddle-like arms well-adapted for swimming.[13] Adult green turtles grow to 1.5 metres (5 ft) long.[14] While individuals have been caught that reached weights of up to 315 kilograms (690 lb), the average weight of mature individuals is 110–190 kilograms (240–420 lb). The largest known C. mydas weighed 395 kilograms (870 lb).[15] Anatomically, a few characteristics distinguish the green turtle from the other members of its family. Unlike the closely related hawksbill turtle, the green turtle's snout is very short and its beak is unhooked. The sheath of the turtle's upper jaw possesses a denticulated edge, while its lower jaw has stronger, serrated, more defined denticulation. The dorsal surface of the turtle's head has a single pair of prefrontal scales. Its carapace is composed of five central scutes flanked by four pairs of lateral scutes. Underneath, the green turtle has four pairs of inframarginal scutes covering the area between the turtle's plastron and its shell. Mature C. mydas front appendages have only a single claw (as opposed to the hawksbill's two), although a second claw is sometimes prominent in young specimens.[16] The carapace of the turtle has various color patterns that change over time. Hatchlings of C. mydas, like those of other marine turtles, have mostly black carapaces and light-colored plastrons. Carapaces of juveniles turn dark brown to olive, while those of mature adults are either entirely brown, spotted or marbled with variegated rays. Underneath, the turtle's plastron is hued yellow.C. mydas limbs are dark-colored and lined with yellow, and are usually marked with a large dark brown spot in the center of each appendage.[2][17] Ecology and behavior As one of the first sea turtle species studied, much of what is known of sea turtle ecology comes from studies of green turtles. The ecology of C. mydas changes drastically with each stage of its life history. Newly emerged hatchlings are carnivorous,pelagic organisms, part of the open ocean mininekton. In contrast, immature juveniles and adults are commonly found in seagrass meadows closer inshore as herbivorous grazers. Habitat Green sea turtles move across three habitat types, depending on their life stage. They lay eggs on beaches. Mature turtles spend most of their time in shallow, coastal waters with lush seagrass beds. Adults frequent inshore bays, lagoons and shoals with lush seagrass meadows. Entire generations often migrate between one pair of feeding and nesting areas.[13] Turtles spend most of their first five years in convergence zones within the open ocean.[3][35] These young turtles are rarely seen as they swim in deep, pelagic waters.[36][37] Green sea turtles typically swim at 2.5-3kph (0.7-0.8 m/s).[38] Predators Only human beings and the larger sharks feed on C. mydas adults. Specifically, tiger sharks (Galeocerdo cuvier) hunt adults inHawaiian waters.[39] Juveniles and new hatchlings have significantly more predators, including crabs, small marine mammals andshorebirds.[2] In Turkey, their eggs are vulnerable to predation by red foxes and golden jackals.[40] Life cycle Green sea turtles migrate long distances between feeding sites and nesting sites; some swim more than 2,600 kilometers (1,600 mi) to reach their spawning grounds. Mature turtles often return to the exact beach from which they hatched. Females usually mate every two to four years. Males, on the other hand, visit the breeding areas every year, attempting to mate.[41] Mating seasons vary between populations. For most C. mydas in the Caribbean, mating season is from June to September.[13] The French Guiana nesting subpopulation nests from March to June.[20] In the tropics, green turtles nest throughout the year, although some subpopulations prefer particular times of the year. In Pakistan,Indian Ocean turtles nest year-round, but prefer the months of July to December.[32] Green sea turtles mating is similar to other marine turtles. Female turtles control the process. A few populations practice polyandry, although this does not seem to benefit hatchlings.[42] After mating in the water, the female moves above the beach's high tide line, where she digs a hole with her hind flippers and deposits her eggs. Clutch size depends on the age of the female and species, but can range between 100 and 200. She then covers the nest with sand and returns to the sea.[2] At around 45 to 75 days, the eggs hatch during the night, and the hatchlings instinctively head directly into the water. This is the most dangerous time in a turtle's life. As they walk, predators, such as gulls and crabs, grab them. A significant percentage never make it to the ocean. Little is known of the initial life history of newly hatched sea turtles.[13] Juveniles spend three to five years in the open ocean before they settle as still-immature juveniles into their permanent shallow-water lifestyle.[36][37] It is speculated that they take twenty to fifty years to reach sexual maturity. Individuals live up to eighty years in the wild.[2] Each year on Ascension Island in the South Atlantic, C. mydas females create 6,000 to 15,000 nests. They are among the largest green turtles in the world; many are more than a meter in length and weigh up to 300 kilograms (661 lb).[43] Breathing and sleep Sea turtles spend almost all their lives submerged, but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. The lungs permit a rapid exchange of oxygen and prevent gases from being trapped during deep dives. Sea turtle blood can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. During routine activity, green and loggerhead turtles dive for about four to five minutes, and surface to breathe for one to three seconds. Turtles can rest or sleep underwater for several hours at a time, but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles quickly drown in shrimp trawlers and other fishing gear.[16] Conservation In recent decades, sea turtles have moved from unrestricted exploitation to global protection, with individual countries providing additional protection, although serious threats remain unabated. Threats Human action presents both intentional and unintentional threats to the species' survival. Intentional threats include continued hunting and egg harvesting. More dangerous are unintentional threats, including boat strikes, fishermen's nets that lack turtle excluder devices, pollution and habitat destruction. Chemical pollution may create tumors;[48]effluent from harbors near nesting sites may create disturbances; and light pollution may disorient hatchlings. Habitat loss usually occurs due to human development of nesting areas. Beach-front construction, land "reclamation" and increased tourism are examples of such development.[2][3] An infectious tumor-causing disease,fibropapillomatosis, is also a problem in some populations. The disease kills a sizeable fraction of those it infects, though some individuals seem to resist the disease.[12][49][50] Because of these threats, many populations are in a vulnerable state. Pacific green turtle’s foraging habitats are poorly understood and mostly unknown.[51]These foraging grounds are most likely along the coast of Baja California, Mexico and southern California,[52] in which these turtle’s have a high risk of incidental capture by coastal fisheries. The main mortality factor for these turtles is the shrimp trawlers in Mexico, in which many of these turtles go undocumented.[52] The only foraging area that has been identified is the San Diego Bay, but it is heavily polluted with metals and PCBs.[52] These contaminants have a negative effect on the ocean environment, and have been shown to cause lesions and sometimes mortality.[52] Green turtles also are threatened by entanglement and ingestion of plastic.[52] In San Diego Bay, an adult green turtle was found dead with monofilament netting tightly packed in its esophagus.[52]